Dental angles are used by dentists to clean or polish teeth. To accomplish this, dental angles carry dental bits such as prophy cups and brushes and burs. The angle allows dentists to more easily reach various surfaces of a patient's teeth when cleaning or polishing. Angles generally include a body, having a head, which has a major axis angled relative to a major axis of the body. The angle is usually ninety degrees. A drive gear and a driven gear are carried in the body in a meshing relationship. A cap slips over the driven gear and attaches to the body in order to secure the gears within the body. The driven gear generally extends out of an opening in the top of the cap, and carries a desired dental bit, which is used during the cleaning or polishing process. The body is slipped over the nose of a handpiece such as a Doriot type handpiece having a collet which receives the shaft of the drive gear. The collet holds the shaft, and thus the angle, against axial movement. It also connects the drive gear to a motor to rotate the drive gear, which in turn rotates the driven gear and thus the dental bit.
In the past, dentists used nondisposable metal angles. While these were sturdy, they required extensive care to ensure against transferring disease and germs from one patient to another. In use, the head of the angle is inserted into the patient's mouth. This puts the angle into contact with bodily fluid such as saliva and blood. If the metal angle is not properly sealed, the bodily fluids can penetrate the angle. Simply wiping down the metal angle between uses is not adequate sterilization. To properly sterilize the metal angles, the angles must be autoclaved. Additionally, the metal angles must be disassembled periodically and cleaned in order to remove any grit which may have gotten into the angle. If the grit is not removed, it might interfere with the gears, reducing the operating life of the metal angle or making it difficult to operate. Metal angles also require periodic lubrication to ensure their gears run smoothly, quietly, and efficiently to reduce heat build-up. Thus, the care required for metal angles is quite extensive.
Due to the extensive care required by nondisposable angles, disposable ones were desired by dentists. Disposable angles are much more sanitary than nondisposable ones, and therefore more useful in preventing cross-contamination between patients. Their disposable nature eliminates the need to thoroughly sanitize them between each use.
While disposable angles have provided economic and ergonomic benefits in the past, they have not been without problems. The angles often make unwanted noise caused by contact between the drive gear and the shaft of the driven gear. This leads to an unpleasant dental experience for the patient who may already be feeling anxious. Additionally, the unwanted contact causes a rough operation of the gears as opposed to a desired smooth operation. It also causes unnecessary wear and tear on the angle gears, and dentists may need to dispose of the angle sooner than should be necessary. This problem is seen in the angle disclosed in U.S. Pat. No. 5,531,599 (“the '599 Patent”), which is incorporated by reference herein. There is nothing to secure the drive gear within the body. The drive gear is essentially floating within the body. Thus, the angle of the '599 Patent is subject to undesirable noise and vibration caused by unwanted contact between the drive gear and the shaft of the driven gear.
U.S. Pat. No. 5,730,595 (“the '595 Patent”) which is incorporated herein by reference, and which is assigned to the same assignee as the present application, discloses a disposable dental prophylaxis angle. The '595 Patent attempts to solve the problems associated with unwanted contact between the drive gear and the shaft of the driven gear by including a finger located on the cap. The finger fits into a groove near the top of the drive gear. The finger extends down from the cap that fits over the head to hold the gears in place. The finger is aimed to prevent axial movement of the drive gear and shaft. However, the finger is located at the top of the angle as opposed to the bottom of the angle. Thus, the finger does not provide axial support for the drive gear. Axial support is desired because the meshing of the gears happens near the top of the angle, creating a downward force on the drive gear. Thus, the finger does not fully accomplish its goal of eliminating unwanted contact between the drive gear and the driven gear shaft. Therefore, an inexpensive disposable angle, which both secures the drive gear within the body and prevents over-flexing of the shaft is needed.
Contra-angles are a specific type of dental angle often used by dentists and hygienists to reach difficult spots on the teeth. Generally, contra-angles include a head angled at an angle greater than ninety degrees. The body is bent at an angle such that the drive gear shaft is bent within the body. The '599 Patent discloses various parts of a disposable dental prophylaxis contra-angle in FIGS. 7-13 thereof. One drawback with contra-angles, such as the one disclosed in the '599 Patent, is that the bending of the shaft makes the shaft susceptible to breakage. During use, the shaft is rotated, and the bending can cause it to over-flex. This over-flexing leads to breakage of the shaft. Additionally, over-flexing of the shaft may cause the shaft to become disengaged from a dental handpiece to which it is attached. Because the inside of the angle body is generally hollow, the shaft has nothing to secure it within the body. If the shaft becomes disengaged, the dental procedure will be disrupted. Therefore, a dental angle which eliminates the problems associated with over-flexing of the drive gear shaft of a contra-angle is needed.